Why it is "huge amount of work" ? Do the code reliably breaks in every new python version ?

Yes, in python they break something at every release now. It's terrible. It mostly is because they remove modules from their standard library for no good reasons.

For example they've removed asyncore, their original loop-based module before the async/await syntax existed. All the software from that era needs a total rewrite. Luckily in debian for now the module is provided as a .deb package so I didn't have to do the total rewrite.

edit: as usual on ycombinator, dowvotes for saying something factually true that can be easily verified :D